A horizontal type continuous casting machine for casting molten steel into a cast steel strand has recently been industrialized. In this casting machine, molten steel directed from a tundish to a horizontal mold is intermittently and continuously withdrawn into a cast steel strand in the horizontal direction through the horizontal mold by means of a plurality of cycles each comprising a pull and a push.
The above-mentioned conventional horizontal type continuous casting machine is described below with reference to FIG. 1. In FIG. 1, 1 is a tundish for receiving molten steel. A horizontal metal mold 6 is connected through a front nozzle 3, a feed nozzle 4 and a break ring 5 to an opening 1A provided in the lower portion of a side wall of the tundish 1. The upstream end of the front nozzle 3 is inserted into the opening 1A of the tundish 1, and the downstream end of the front nozzle 3 is connected to the upstream end of the feed nozzle 4. The downstream end of the feed nozzle 4 is connected to the upstream end of the break ring 5, and the downstream end of the break ring 5 is connected to the inlet end 6A of the horizontal mold 6. Thus, the opening 1A of the tundish 1, the front nozzle 3, the feed nozzle 4, the break ring 5 and the horizontal mold 6 form a horizontal passage for molten steel.
The break ring 5 has the function of forming a sure starting point of solidification of molten steel 2 introduced from the tundish 1 through the front nozzle 3, the feed nozzle 4 and the break ring 5 into the horizontal mold 6, and thus ensuring smooth withdrawal of a cast steel strand 7 from the horizontal mold 6. The inlet end 6A of the horizontal mold 6 is formed so as to match with the tapered outer surface 5A of the break ring 5, and the outer surface 5A of the break ring 5 comes into a liquid-tight contact with the inlet end 6A of the horizontal mold 6 by urging the break ring 5 toward the horizontal mold 6 by means of the feed nozzle 4. The horizontal mold 6 is made of copper or a copper alloy added with beryllium, and has therein a cooling water passage 6B. Cooling water circulates through the cooling water passage 6B to cool the horizontal mold 6.
At least one pair of pinch rolls (not shown) and a cooling zone (not shown) are arranged following the horizontal mold 6. The at least one pair of pinch rolls intermittently and continuously withdraws molten steel 2 directed to the horizontal mold 6 into a cast steel strand 7 in the horizontal direction through the horizontal mold 6 by means of a plurality of cycles each comprising a pull and a push. The cooling zone cools the cast steel strand 7 thus withdrawn from the horizontal mold 6.
According to the above-mentioned conventional horizontal type continuous casting machine, the cast steel strand 7 is manufactured as follows. Molten steel 2 received in the tundish 1 is introduced through the front nozzle 3, the feed nozzle 4 and the break ring 5 into the horizontal mold 6. Molten steel 2 introduced into the horizontal mold 6 is intermittently and continuously withdrawn into the cast steel strand 7 in the horizontal direction through the horizontal mold 6 by the at least one pair of pinch rolls (not shown). Then, the cast steel strand 7 thus withdrawn from the horizontal mold 6 is cooled while passing through the cooling zone (not shown). The cast steel strand 7 is thus continuously cast.
In the above-mentioned conventional horizontal type continuous casting machine, the break ring 5 has the function of forming a sure starting point of solidification of molten steel introduced into the horizontal mold 6. It is therefore important to liquid-tightly connect the outer surface 5A of the break ring 5 with the inlet end 6A of the horizontal mold 6 so as not to produce a gap therebetween. If a gap is produced between the outer surface 5A of the break ring 5 and the inlet end 6A of the horizontal mold 6, deposited metal formed by solidification of molten steel 2 penetrating into this gap during casting is caught by the gap, and this causes breakage of a solidified shall 7A of the cast steel strand 7 during pull thereof, thus imparing smooth formation of the solidified shell 7A. Defects are produced as a result on the surface of the cast steel strand 7 and may cause breakout of molten steel 2 and breakage of the break ring 5.
It is therefore the conventional practice, when replacing the break ring 5, to conduct a fitting operation by repeatedly trying to fit the outer surface 5A of the refractory break ring 5 to the inlet end 6A of the horizontal mold 6 upon every grinding of the outer surface 5A of the break ring 5 so that a gap is not produced between the outer surface 5A of the break ring 5 and the inlet end 6A of the horizontal mold 6, in order to ensure a liquid-tight connection of the downstream end of the break ring 5 to the inlet end 6A of the horizontal mold 6. However, it is not easy to verify, in the assembled state of the horizontal mold 6 into the line, that no gap is produced between the outer surface 5A of the break ring 5 and the inlet end 6A of the horizontal mold 6. Consequently, the fitting operation of the break ring 5 requires much labor and time, and it is not easy to liquid-tightly connect the downstream end of the break ring 5 to the inlet end 6A of the horizontal mold 6.
Under such circumstances, there is a strong demand for the development of a horizontal type continuous casting machine for casting molten steel into a cast steel strand, which permits an easy and liquid-tight connection of the downstream end of the break ring 5 to the inlet end 6A of the horizontal mold 6 in a short period of time by facilitating the above-mentioned fitting operation of the break ring 5, but a horizontal type continuous casting machine provided with such properties has not as yet been proposed.